pontoon prop question

[mhcooper84]

I have a 2003 22 ft crest pontoon it goes 15 knots at 4300 rpm's wot what size prop do you think would be best on this type boat? it is a 70 evinrude and weighs about 2300 lbs

 

[MH Hawker]

Re: pontoon prop question

you will need to know what the motor max rpm is and what pitch the present prop is also.

 

[mhcooper84]

Re: pontoon prop question

my boat maxs 4800 factor says 5500 also the pro is 14 x 13

 

[westwinds]

Re: pontoon prop question

Propeller Handbook by Dave Gerr has a rule of thumb on page 45 that states engine speed will increase about 450 RPM for every two inch decrease in propeller pitch. If wide open throttle (wot) gives 4800 RPM and the engine is good for 5500 RPM, then the pitch should be decreased by 3 or a 14X10 propeller. A one inch decrease in diameter would also give about the same results, but with reduced efficiency. You have to experiment some to get the right size so try and find someone who will allow you to try several propellers on an exchange basis.

 

[MH Hawker]

Re: pontoon prop question

Not sure if they make a 10 P but they do make a 11 P and yes see if you can find a shop with test props. And a 11 P should put you in the right range.

 

[BobGinCO]

Re: pontoon prop question

Propeller Handbook by Dave Gerr has a rule of thumb on page 45 that states engine speed will increase about 450 RPM for every two inch decrease in propeller pitch.

That's a VERY iffy rule of thumb.
WHen I took my Merc 115 from a 15 inch pitch to a 13 inch pitch, by that thinking I would have increased my WOT RPM from 4800 to 5250. Instead it increased to 6200!

 

[Water logged]

Re: pontoon prop question

A 950 rpm increase with a 2" pitch change seems very extreme. Were there any other changes made?

 

[MH Hawker]

Re: pontoon prop question

Pontoons are a good bit different than other boats when it comes to RPM vs pitch changes. It is a lot cheaper to find a shop that has test props vs buying them to experiment with at 150.00 a pop it gets expensive real quick.

I would try a 11 P first and maybe a 9 P.

2300 sounds a bit heavy to me on weight my 20 foot boat with gear is around 1500, but I am hardly a expert on such things but in the end its RPM that matters.

 

[BobGinCO]

Re: pontoon prop question

A 950 rpm increase with a 2" pitch change seems very extreme. Were there any other changes made?

Well, I DID lose 3 or 4 pounds between runs... Other than that, no.